1. Field of the Invention
The present invention relates to a shoe with a breathable sole.
2. Description of the Related Art
It is known that, in order to ensure hygienic and comfortable conditions for the feet, a shoe should not trap the products of perspiration (moisture and water vapour) but, on the contrary, should prevent stagnation thereof. This requirement is all the greater if the foot is subject to overheating or to stresses (for example sporting activities). Obviously the strength and the protection provided by the shoe must not be compromised in the attempt to make a shoe breathable.
Many solutions which aim to obtain a shoe which is both breathable as well as comfortable and safe are known. Patent application WO 04/028284 describes a sole comprising:
a support layer which in at least one macro-portion is made of “perforated” material;
a breathable membrane associated on top of the support layer at least in the macro-portion;
a tread made of plastic material with a macro-perforation at least at the macro-portion, the tread being joined hermetically to the membrane and to the support layer at least along the perimeter of the macro-portion.
The patent application WO 02/32246 attempts to solve the technical problem whereby, in a sole comprising a layer of felt to which a breathable membrane is joined, the latter tears because it is not sufficiently elastic with respect to the felt layer. The solution consists in providing an inner sole which has a layer preventing elongation of the felt situated underneath the membrane. These three layers are provided in sandwich form and communicate with the exterior by means of holes formed in the tread of the shoe.
In patent application WO 98/51177 the technical problem is that of improving the process for manufacturing a breathable shoe and ensuring that the associated breathable membrane is protected from mechanical stresses. A tread is provided with perforations and is in contact with an insole which comprises a membrane associated above a protective layer so as to form a stratified or sandwich structure. The insole is pre-moulded and assembled with the tread using glue or by means of overinjection.
In patent EP 1,089,642 the technical problem is that of increasing the circulation (otherwise poor) of air inside the shoes, while protecting the breathable membrane which renders the shoe breathable. It is considered that the poor circulation is due to the small number of perforations in the shoe with respect to its surface area, so that the solution proposed is a sole with an integrated tread in which raised vertical projections in an empty region are in contact with a protective layer on top of which a membrane is associated. The empty region communicates with the exterior of the shoe via numerous horizontal channels.
In the patent application WO 02/14326 the technical problem is to provide a breathable shoe. This patent describes a shoe which has an insole comprising a membrane associated with an underlying protective layer in turn joined to a perforated tread, all of which with a sandwich structure. A perforated filling layer or “filler” is arranged on the membrane. By way of a variation of assembly, the edges of the membrane may be also joined directly to the tread.
All these solutions have intrinsic disadvantages. The sandwich structure which includes the breathable membrane is commonly fixed to the remainder of the shoe by means of overinjection of plastic material which forms the tread. There is therefore the risk of damaging the membrane which per se is very delicate and does not withstand very well the aggressive action of the melted plastic material. Another very important disadvantage is that the expulsion of the moisture from inside the shoe through the membrane may take place only naturally, namely that the moisture must pass through the membrane spontaneously. This is a very slow natural process; a forced process which increases the efficiency thereof would be advantageous.